1. Field of the Invention
The present invention generally relates to conductive straps utilized to connect storage devices to transistors and more particularly to self-aligned near surface straps for high density trench storage devices.
2. Description of the Related Art
Conventional systems for processing trench dynamic random access memory (DRAM) structures form a buried strap by performing two recess steps and etching the collar after the first of these recesses. The second recess provides margin for a dielectric on top of the trench to isolate it from the passing wordline. In this scheme, the buried strap depth (determined by the sum of the first recess and collar wet etch) cannot be made very shallow and is thus not scalable from standard device scaling rules, which as is well known in the art, require shallow junctions. Secondly, the difference in two recess depths combined with the required presence of a thin interface (to prevent dislocations) places severe constraints on the tolerance of the resistance contributed by the buried strap.
Several suggestions have been made to ameliorate some of the problems mentioned above including methods to form the buried strap after active area (AA) definition (which adds considerable cost), a divot strap (which can cause a large pad oxide undercut), and a surface strap (which places considerable pressure on isolation planarization). Therefore, there is a need for a strap that allows better control of the leakage of current from the capacitor and is thus much more scalable.
It is, therefore, an object of the present invention to provide a structure and method for a dynamic random access memory device comprising a storage trench, a storage conductor within the storage trench, a lip strap connected to the storage conductor, and a control device electrically connected to the storage conductor through the lip strap. The trench contains a corner adjacent the control device and the lip strap and has a conductor surrounding the corner. The control device has a control device conductive region adjacent the trench and the lip strap and has a conductor extending along a side of the trench and along a portion of the control device conductive region. In addition, the device can have a collar insulator along a top portion of the trench, wherein the lip strap includes a conductor extending from a top of the collar to a top of the trench. The lip strap can also extend along a surface of the device adjacent the trench and perpendicular to the trench. A node dielectric, lining the trench where the lip strap surrounds an upper portion of the node dielectric, is adjacent the top portion of the trench and can have a trench top oxide where the lip strap extends into the trench top oxide and forms an inverted U-shaped structure. Further, the lip strap can include a conductor extending along two perpendicular portions of a top corner of the trench.
The invention further includes a method of forming a dynamic random access memory structure for forming a trench within a substrate, filling the trench with a trench conductor, forming a pad oxide along a surface of the substrate adjacent the trench, forming a collar along an upper portion of the trench such that the collar insulates the substrate from the trench conductor, recessing the collar and the pad oxide, depositing a lip strap over the trench conductor and in recesses produced by the recessing, and forming an isolation region adjacent the lip strap.